Fire and police union leaders Wednesday criticized a new proposal by Mayor Bill de Blasio to improve disability benefits for newer members hurt on the job as "unacceptable," saying his plan still leaves in place a disparity with more senior employees.

De Blasio's office wants to change state law to boost benefits available to uniformed officers of the NYPD, FDNY, Department of Correction and Department of Sanitation hired in recent years and injured on the job.

"This bill will ensure every uniformed worker -- especially those just starting out on the job -- is protected by this city after a tragic injury," de Blasio said in a statement.

But it does not provide them the same protections -- 75 percent of their final salary in addition to their full Social Security benefits -- as more senior officers. The lower tier applies to police and firefighters hired after July 2009, and to sanitation and correction officers hired after April 2012.

Patrolmen's Benevolent Association president Patrick Lynch and Uniformed Firefighters Association president Steve Cassidy said they learned late Wednesday afternoon about the proposal from Deputy Mayor Anthony Shorris while de Blasio was out of town.

"Based upon that brief, last-minute phone conversation, the plan is unacceptable," the union leaders said in a joint statement. The proposal, they said, doesn't change a "two-tiered disability structure with some police officers and firefighters having adequate disability protections and others with inferior benefits."

Those in the lower-experience tier who suffer disabling work injuries receive half the average of their final three or five years of pay, depending on the department -- a sum offset and reduced by an amount equal to half their Social Security benefits.